Local surface roughness of cylindrical gears: Concept, method, and application

Abstract

Surface roughness strongly affects the surface load-carrying capacity, transmission efficiency, and bending strength of gears. However, tooth-surface roughness is traditionally measured in terms of the average roughness parameter of the tooth surface, which is satisfactory for processing quality control but inadequate for performance analysis purposes. Each point of the tooth-profile meshes sequentially and its parameters (such as slip–roll ratio, load, and friction) temporally vary throughout the gear transmission process. Considering these variations, this paper proposes a local roughness and evaluation method for analyzing tooth-profile wear. First, the gear-tooth profile (roughness, waviness, and shape deviation) is obtained on multiple geometric scales using a roughness profilometer. Second, the acquired curves are mapped to the gear coordinate system using the orthogonal distance fitting algorithm. Thereafter, the contact of the tooth surface is analyzed under the working conditions of a gear pair. The Hertzian contact width of the working points of the tooth profile is calculated from the root to the top of the tooth, and the roughness parameter at each point is calculated in the contact area. The obtained roughness parameters are sequentially connected to obtain the local roughness curve. Finally, the tooth profile wear is determined from the local roughness curve during an FZG gear test. The local roughness curves provide accurate evaluations of the lubrication state of the tooth surface and the locations of pitting and micro-pitting on the tooth surface.